Why are you doing this?
Joomla is one of the very best there is since 2 decades. I'm just trying to convince you to stop doubting and feel confident about the choice you're about to make.
If you want to break free right away and sail an independent journey, you are on the right track. Extensions like the Phoca Cart e-commerce are there for the long run, for sure. They are built with care, maintained well all the way and have every functionality you need, every time, all the time.